A typical powered torque device used for making up or breaking out pipe connections in oilfield-related applications includes a pair of torque device members, here termed “first torque device member” and “second torque device member”, but often referred to as “power tong” and “backup tong.” In use, the power tong rotates a first pipe relative to a second pipe while the backup tong holds the second pipe relatively stationary. Each of these tongs has a slot for receiving its respective pipe. Typically, each of these tongs has a set of clamp bodies that normally includes clamp dies for engaging the pipe when the pipe is received in the tong slot.
In some powered torque devices, the torque applied to the first pipe by the power tong is derived from a pair of push-pull hydraulic actuators. These powered torque devices typically impose significant shear loads on the pipe connection as a result of inherent push-pull force imbalance of the push-pull hydraulic actuators and eccentricity of the backup and power tongs induced by tong clamping error. These shear loads can contribute to improper make-up of pipe connections. In these powered torque devices, lateral loads on the threads of the pipe connection can change the friction in the pipe connection and cause some degree of torque masking. Here, the term “torque masking” refers to anything that causes the torque reading from the powered torque device to deviate from the actual torque experienced by the pipe connection.
In some powered torque devices, mechanical guiding is used between the backup and power tongs to ensure that the backup tong and power tong have a common pipe rotation axis while the power tong is rotating. The guiding typically takes the form of a system of guide rings concentric to a theoretical pipe axis and arranged between the backup tong and the power tong and/or between the power tong and an outer structure. The current-art guide system will typically work during torque application when both the backup and power tongs are clamped to the pipes and during non-torque rotation when the power tong is not clamped to a pipe. In these powered torque devices, clamp center deviation between the power and backup tongs can cause torque masking. Specifically, if the clamped center deviation exceeds the guide ring clearance, some portion of the clamping force will be transferred onto the guide ring surfaces. The resulting friction during rotation of the power tong will then function as a drum brake leading to an apparent torque larger than the actual torque.
Errors in torque reading can make it difficult to make-up pipe connections with accuracy, particularly in applications where pipe connections are to be made up with torque in a narrow torque bandwidth.
The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art.
The object is achieved according to the invention by virtue of the features disclosed in the description below and in the subsequent claims.